These have the chemical stability of platinum, but increased hardness.

Due to its high density, hardness, and resistance to corrosion, platinum-iridium was used to make the international prototype kilogram and the international prototype meter.

One use for Pt/Ir alloy is fabrication of metal microelectrodes for electrical stimulation of nervous tissue and electrophysiological recordings. Pure iridium is very difficult to pull into small diameter wires, while pure platinum has a low Young's modulus which makes pure platinum wires bend easily during the insertion in nervous tissue; hence Pt/Ir alloy has an optimal combination of mechanical and electrochemical properties for this application.